“I have had dogs since I was a boy and loved them all dearly, including Martha who was my companion for about 15 years and about whom I wrote the song ‘Martha, My Dear.'”

Paul has joined forces with PETA to petition to the parent company of The Pet Blood Bank’s distributor, Patterson Veterinary Supply, to provide proper care for some 150 greyhounds living in squalor in dirt-floored pens. On Tuesday (Oct. 10), Paul penned a letter appealing for better treatment of the animals.

“I join my friends at PETA in asking you to pay these greyhounds back, and to let them retire from the dirt-floored, barren conditions in which they are kept isolated and alone, some of them cringing at the footfall of the person coming to take their blood again and again,” Paul wrote. “They had a hard life on the racetrack, and they will die without love if left where they are. I’ve seen pictures of how they have suffered from nails that have grown back into their paw pads, as well as from infected gums and rotted teeth, and I’m told that some have apparently even died from a lack of water.”

The Pet Blood Bank provides canine blood products for veterinary transfusions across the country. It began in 2004 initially seeking volunteers and using a bloodmobile, but that did not bring in enough blood and the company turned to retired greyhounds it houses in a kennel on a private farm outside Austin, Texas.

Following an exposé by PETA and coverage by the Washington Post last month that detail shocking conditions with photos showing the greyhounds in bad shape with overgrown nails, emaciated figures and tartar-filled teeth, The Pet Blood Bank, Inc. had promised to ensure the dogs’ care, according to a PETA spokesperson, but reneged on that pledge. That prompted McCartney to write his letter to parent company Patterson Companies CEO James Wiltz.

“I have had dogs since I was a boy and loved them all dearly, including Martha who was my companion for about 15 years and about whom I wrote the song ‘Martha, My Dear,'” wrote Paul about the classic Beatles track. “I’m sure you know that dogs need affection and comfort—a bed to lie on, warmth in the winter, the opportunity to run and play, and just like you and me, they crave happiness and companionship.”

Paul has been a longtime supporter of PETA, participating in interviews on the animal rights organization’s website and featuring in pro-vegetarian ads.

Read his full letter here:

Dear Mr. Wiltz,

I am writing to appeal to you to step up, make good on your earlier pledge, and rescue the dogs whose blood your company has used for many years, knowing that these 150 or so dogs—who were allowed to get into appalling shape and who are now kept in a-mile­less-than-ideal conditions—helped your business at a cost to their wellbeing.

I have had dogs since I was a boy and loved them all dearly, including Martha who was my companion for about 15 years and about whom I wrote the song “Martha, My Dear.” I’m sure you know that dogs need affection and comfort—a bed to lie on, warmth in the winter, the opportunity to run and play, and just like you and me, they crave happiness and companionship.

I join my friends at PETA in asking you to pay these greyhounds back, and to let them retire from the dirt-floored, barren conditions in which they are kept isolated and alone, some of them cringing at the footfall of the person coming to take their blood again and again. They had a hard life on the racetrack, and they will die without love if left where they are. I’ve seen pictures of how they have suffered from nails that have grown back into their paw pads, as well as from infected gums and rotted teeth, and I’m told that some have apparently even died from a lack of water.

Good people, professional greyhound rescuers, are standing by to place these dogs in good homes and to transport them to those homes at no cost to anyone. Please do the right thing and win the support of all kind veterinarians and all kind souls the whole world over.